In recent years various methods have been devised for treating cellulosic fiber-containing products, such as cloth made of cotton or cotton blends, in order to impart durable crease retention, wrinkle resistance and smooth drying characteristics thereto. For example, cellulosic materials have been crosslinked with formaldehyde, giving durable crosslinks having good resistance to repeated laundering and also to various acids and alkalis, and chlorine bleaches. These formaldehyde treated cellulosic materials are resistant to discoloration and yellowing, and are less likely to produce a rash or other sensitization on the wearer than cellulosic materials treated with resins or precondensates of the urea-formaldehyde or substituted urea-formaldehyde types which may decompose and release formaldehyde while in use.
However, while formaldehyde has made a significant contribution to the cotton finishing art, the results have been far from perfect. For instance, in some cases the formaldehyde crosslinking treatment has tended to lack reproducibility, since control of the formaldehyde crosslinking reaction heretofore has been difficult. When high curing temperatures were used with an acid or potential acid catalyst, overreaction and degradation of the cotton often happened which considerably impaired its strength. On the other hand, when attempts were made to achieve reproducibility at temperatures of 50.degree. C. or less, much longer reaction or finishing times were usually required, rendering the process economically relatively unattractive. This has been particularly true when sulfur dioxide was used as a catalyst in the previously known processes such as that disclosed in U.S. Pat. No. 3,663,974 or the corresponding British Pat. No. 980,980. In other cases, formaldehyde cross-linking has not been able to meet commercial standards with respect to dry wrinkle recovery. For these and similar reasons efforts have been continuing to develop new and better finishing processes for cotton and other cellulose fiber materials.
For the sake of completeness it may also be mentioned that it has been previously suggested in U.S. Pat. No. 2,870,041 that formaldehyde odors in fibrous material which has been treated with a urea-formaldehyde or melamine-formaldehyde type crosslinking resin can be prevented by treating such material with an aqueous solution of sodium meta bisulfite or of some sulfite or bisulfite salt which supplies HSO.sub.3.sup.- ions to the system and forms a stable addition product with formaldehyde.
However, in such a system formaldehyde is not used as the creaseproofing agent and the "stabilization" of the formaldehyde in the system does not serve to creaseproof it. On the contrary, a customary dry high temperature cure of the material containing the melamine-formaldehyde or other crosslinking resin in the presence of a latent curing catalyst is required, which in turn requires removal of the salt catalyst from the cured fabric by washing. The possibility of using sulfur dioxide in aqueous solution as the formaldehyde-binding agent is also suggested in said U.S. Pat. No. 2,870,041. However, as only an unstable hydroxy methyl sulfonic acid is formed from formaldehyde and sulfur dioxide in the presence of water and this acid reverts to formaldehyde and sulfur dioxide on drying, it is evident that this previously suggested use of aqueous sulfur dioxide can not serve as an effective means either for the permanent removal of formaldehyde odors nor for any other significant improvement of the resin-treated material.